Radio observations of the Ursa Major II dwarf spheroidal galaxy obtained using the Green Bank Telescope are used to place bounds on weakly interacting massive particle (WIMP) dark matter properties. Dark matter annihilation releases energy in the form of charged particles which emit synchrotron radiation in the magnetic field of the dwarf galaxy. We compute the expected synchrotron radiation intensity from WIMP annihilation to various primary channels. The predicted synchrotron radiation is sensitive to the distribution of dark matter in the halo, the diffusion coefficient $D_0$, the magnetic field strength $B$, the particle mass $m_{\chi }$, the annihilation rate $⟨{\sigma }_{\mathrm{a}}v⟩$, and the annihilation channel. Limits on $⟨{\sigma }_{\mathrm{a}}v⟩$, $m_{\chi }$, $B$, and $D_0$ are obtained for the $e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, ${\tau }^{+}{\tau }^{-}$, and $b\overline{b}$ channels. Constraints on these parameters are sensitive to uncertainties in the measurement of the dark matter density profile. For the best fit halo parameters derived from stellar kinematics, we exclude 10 GeV WIMPs annihilating directly to $e^{+}{e}^{-}$ at the thermal rate $⟨{\sigma }_{\mathrm{a}}v⟩=2.18\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$ at the $2\sigma$ level, for $B>0.6\mu \mathrm{G}$ ($1.6\mu \mathrm{G}$) and $D_0=0.1(1.0)\times$ the Milky Way diffusion value.

• Received 26 August 2013

DOI:https://doi.org/10.1103/PhysRevD.88.083535